An important aspect of modern electronics packaging is increasing the component density. A compact packaging technology is needed when mounting area is limited, dictating that circuit elements be closely spaced. Modules containing a number of semiconductor devices are used to densely place semiconductor devices and to obtain a small-sized electronic device.
In multiple chip modules die may be supplied as either bare untested, unburned-in die or supplied at greater expense as tested, burned in die. If one of the die fails in a multiple chip module using bare die, the entire module may be lost because the replacement procedure may not be cost effective or easy to effect. Hence, it is desirable to use tested, burned-in die. However, using tested burned-in die still does not guarantee that a die in the module will not fail and cause the entire module to be rejected. Therefore, prior art methods for fabricating multiple chip modules are relatively costly.
As an alternative to multiple chip modules, rigid-flex board has been used to achieve the form factor of a DRAM SIMM at double density. FIG. 1 shows how a rigid-flex board is mounted in the prior art. Parallel facing panels 10A and 10B are conductively and physically connected to each other at their respective upper ends by conductive trace containing tape 12. Together, panels 10A and 10B make up rigid-flex board 10. DRAM SIMM connector 15 is attached to the bottom edge of panel 10B and conductively and physically connects rigid-flex board 10 to a receptacle (not shown) on printed circuit board 18. Rigid-flex board 10 is used to allow surface mounting of components on four surfaces: 1) the exterior of panel 10A; 2) the exterior of panel 10B; 3) half of the interior of panel 10A; and 4) the half of the interior of panel 10B opposite the unoccupied half of the interior of panel 10A. This utilizes the area of three out of four panel surfaces while retaining a DRAM SIMM profile. The components mounted on rigid-flex board 10 may be burned in and tested prior to mounting to ensure operability.
In general, flexible rigid-flex printed circuit boards can be configured into three-dimensional multiplanar shapes to provide a high density and volume-efficient form of circuitry.